I haven't installed SQL Server 2008 yet.
However I have read that it has a new Merge statement, which does a Insert/Update as appropriate.
My concern is with Triggers on the table.

If you have a Trigger for both Insert & Update, and then execute a Merge, does the trigger fire twice (once for the rows Inserted & once for the rows Updated)?
Or does it just fire once - which would mean that the Deleted "table" would hold some records, but not as many as the Inserted "table".